Heat Integration Research Articles

Integrating direct air capture with algal biofuel production to reduce cost, energy, and GHG emissions

We investigate the potential to reduce costs and greenhouse gas emissions of the utilization of direct air capture of CO2 (DAC) for the production of algal biofuel. We examine four integrated designs for a DAC system comprised of solid amine monolith adsorbents delivering CO2 at the required level for algae cultivation with a photobioreactor (PBR)-based fuel production facility. We show that the integration of DAC with this biofuel production facility provides cost and greenhouse gas emissions benefits. Heat integration decreases operating expenses by reducing energy demand for heating requirements. Mass integration, utilizing flue gas CO2 as a carbon source for the PBRs, decreases the DAC system scale, resulting in both capital and operating cost savings. The most advantageous option depends on the interplay of heat and mass integration while matching the diurnal rhythm of algal growth with the inherently steady pace and energy requirements of the DAC system and fuel production. For these technologies, the DAC-PBR mass and energy integration provides an 18 % cost reduction and a 50 % reduction in greenhouse gas emissions for the current state of the technology.

Synthesis of flexible inter-plant heat exchanger networks: A decomposition method considering intermedium fluid circles

The traditional methods for synthesizing flexible heat exchanger networks (HENs) are not directly applicable to inter-plant HEN challenges, primarily due to the spread of system uncertainty across plants via intermedium fluid circles. This complicates the synthesis process significantly. To tackle this issue, this study proposes a decomposed stepwise methodology to facilitate the flexible synthesis of the inter-plant HENs performing indirect heat integration. A decomposition strategy is proposed to divide the overall network into manageable sub-networks by dissecting the intermedium fluid circles. To address the variability in intermedium fluid temperatures, a temperature fluctuation analysis approach is developed and a heuristic rule is introduced to maintain the temperature feasibility of the intermedium fluids. To ensure adequate flexibility and cost-effectiveness of the designed networks, flexibility analysis and network retrofit steps are conducted through model-based optimization techniques. The efficacy of the method is demonstrated through two case studies, showing its potential in achieving the desired operational flexibility for inter-plant HENs.

Dynamic control analysis of energy-efficient side-stream extractive distillation process for separating close-boiling mixture

To separate the close-boiling mixture comprising heptane and toluene, this study introduces an environmentally-friendly method of side-stream extractive distillation by utilizing aniline as the separating agent. This approach modifies traditional extractive distillation by adding a side rectifier, converting two-way vapor and liquid communication into one-way liquid transfer using an additional distillation section along with corresponding reboiler. Our present study investigates the dynamic control behavior for a strongly non-ideal system without and with heat integration. It focuses on achieving stable and reliable regulatory control by closely keeping the dual-product composition to their original design standards. Key control loops are pinpointed, with a specific emphasis on those centered around adjusting reboiler heat duty and side-stream flow rate within extractive column C1 to regulate the temperatures of Stages 48 and 36. Furthermore, control effectiveness is enhanced by introducing a feedforward action of reboiler heat duty-to-feed flowrate. By developing a new and robust control architecture, high feed flowrate and composition disturbances can be managed efficiently, solving the issues of oscillation and large transient response.

Energy assessment and heat integration of biofuel production from bio-oil produced through fast pyrolysis of sugarcane straw, and its upgrading via hydrotreatment

Sugarcane processing is one of the most important economic activities in Brazil, producing ethanol and sugar for domestic and international markets. Utilising the lignocellulosic residues of this industry, specifically bagasse and straw, would increase the second-generation biofuel production without increasing the sugarcane planted area. Among the processes available, the fast pyrolysis is a thermochemical conversion process that produces mainly bio-oil, a liquid with several advantages over solid biomass, regarding transportation, pumping, storage, and handling. Moreover, the bio-oil can be upgraded to obtain biofuels of higher added-value. Among feasible upgrading technologies, the hydrotreatment is one of the most promising methods for eliminating the reactive functionalities of the bio-oil by removing oxygen or cracking large molecules in the presence of hydrogen; however, this comes at the expense of a significant hydrogen consumption. Thus, the aim of this study is to evaluate the biofuel production through the fast pyrolysis of sugarcane straw, followed by the upgrading of the produced bio-oil via hydrotreatment. The evaluation is carried out by way of energy and mass balances of the processes, performed using the software Aspen Plus. Furthermore, the possibilities of integrating the bio-oil production and upgrading into the conventional ethanol and sugar production process will also be assessed through heat integration, applying the Pinch analysis. Results showed the potential for renewable gasoline and diesel production with yields of 0.086 kg/kg of dry straw and 0.08 kg/kg of dry straw, respectively. Additionally, integrating the pyrolysis process, including the bio-oil upgrading, into the ethanol production process can achieve a liquid fuel production (ethanol, gasoline and diesel) of 2289.8 MJ/t cane, which represents an increase of 29 %, while the surplus electricity increases in 5.3 %, when compared to the conventional ethanol production plant.

Regional variation in the role of humidity on city-level heat-related mortality.

The rising humid heat is regarded as a severe threat to human survivability, but the proper integration of humid heat into heat-health alerts is still being explored. Using state-of-the-art epidemiological and climatological datasets, we examined the association between multiple heat stress indicators (HSIs) and daily human mortality in 739 cities worldwide. Notable differences were observed in the long-term trends and timing of heat events detected by HSIs. Air temperature (Tair) predicts heat-related mortality well in cities with a robust negative Tair-relative humidity correlation (CT-RH). However, in cities with near-zero or weak positive CT-RH, HSIs considering humidity provide enhanced predictive power compared to Tair. Furthermore, the magnitude and timing of heat-related mortality measured by HSIs could differ largely from those associated with Tair in many cities. Our findings provide important insights into specific regions where humans are vulnerable to humid heat and can facilitate the further enhancement of heat-health alert systems.

Sustainable process design and multi-objective optimization of efficient and energy-saving separation of xylene isomers via extractive distillation based on double extractants

The focus of the chemical industry on environmental protection and energy conservation has driven the development of green distillation technology. Xylene isomers are extensively utilized industrial raw materials, whose separation is challenging and energy-intensive due to their closely similar boiling points. Therefore, it is urgent to develop energy-saving and environmental protection technology. In this paper, an energy-saving and environmental protection process for separating the xylene isomers by extractive distillation was designed combing the vapor recompression process with feed preheating (VRAPFP). The parameters of extractive distillation processes were synthetically optimized by multi-objective genetic algorithm (MOGA) with total annual cost (TAC), CO2 emission (ECO2) and separation efficiency (Eext) as the objective evaluation indexes. The economical optimal process was used further for VRAPFP design through heat integration to reduce energy consumption, and all the designed candidate processes were synthetically analyzed, compared and evaluated with performance indexes. Results show that the VRAPFP process has superior economic efficiency and ecological sustainability compared with the existing distillation process, wherein the TAC and ECO2 are reduced by 14.2 % and 30.2 %, respectively. This work provides a new reference and idea for separating xylene isomers with the economy and developing new processes for energy conservation and environmental protection.

Automated hybrid distillation sequence synthesis framework of mixed azeotropes and nonazeotropes

Distillation technology is a crucial, energy-intensive component of energy-supply systems, thereby motivating the improved design of distillation systems. This study investigated an automated framework for synthesizing hybrid distillation sequences, providing a systematic approach for the design and optimization of distillation sequences involving azeotropes. The proposed method separated mixed azeotropes and nonazeotropes by replacing the simple columns in the superstructure of a conventional distillation sequence with extractive distillation columns. The automated calculation of the superstructures was implemented by calling the external interface of the process simulator. The results of these calculations were used to formulate a mixed-integer linear programming problem that was optimized with the objective function of the total annualized cost (TAC). Finally, the optimal solution and all feasible alternatives were obtained. Moreover, the reliability and efficiency of the proposed framework were demonstrated through two case studies. The results show that the separation position of the azeotrope in the sequence and the presence or absence of heat integration significantly impact the TAC of the system. However, using an existing component versus an external component as an entrainer makes very little difference in the TAC for the optimal sequences.

Novel heuristic algorithm incorporating dynamic penalty and adaptive evolution strategy for heat integration network design

Designing efficient heat-exchanger networks is essential for the effective use of energy in the process industries, fostering sustainable and low-carbon development. Traditional heuristic algorithms often fail to balance global and local search processes adequately when solving heat exchanger network synthesis. This frequently leads to early structural fixation and limits the exploration of integer variable search spaces. This study presents an innovative structural enhancement approach, incorporating a dynamic penalty for utility operating costs and an adaptive evolution strategy. The developed method increases the number of heat exchangers by dynamically penalizing utility operating costs and allows evolutionary parameters to be adaptively adjusted based on historical solutions. This approach diminishes the dependence on manual parameter tuning while enhancing flow matching diversity. Moreover, novel metrics for assessing structural diversity, based on node-based nonstructural model with stream splitting are established to facilitate the transition between various optimization paths, thereby improving the algorithm's robustness throughout different stages of the optimization process. Finally, computational analysis on five industrial-scale cases yields more optimal solutions with varied structural configurations compared to previous studies, demonstrating the method's feasibility and effectiveness.

Seasonal thermal energy storage employing solar heat: A case study of Heilongjiang, China, exploring the transition to clean heating and renewable power integration

Seasonal thermal energy storage (STES) offers an attractive option for decarbonizing heating in the built environment to promote renewable energy and reduce CO2 emissions. A literature review revealed knowledge gaps in evaluating the technical feasibility of replacing district heating (DH) with STES in densely populated areas and its impact on costs, fossil fuel consumption, CO2 emission reduction, and renewable power integration. The effects of large-scale STES applications on the power and DH sectors in a regional energy system were quantified by applying the 2030 and 2050 power structure scenarios. The results indicated that STES reduces fossil fuel consumption and CO2 emissions at an affordable cost. It facilitates the integration of wind and solar power into power grids. With 100 % replacement of DH by STES, fossil fuel consumption and CO2 emissions can be reduced by approximately 40 % and 45 % in 2030 and 2050, respectively, with an annual cost increase of 20 %. The CO2 avoidance costs were predicted to be approximately 60 €/t in 2030 and well below 50 €/t in 2050. STES will reduce renewable power curtailment by 10 % in 2030 and 18 % in 2050. This study investigated STES from an energy-system perspective, supporting the formulation of clean heating transition policies.

Simultaneous process optimization and heat integration for ethylene-to-ethylene oxide process: A surrogate model-based approach

Since the production process of ethylene to ethylene oxide (EO) is highly energy-intensive, it is necessary to perform a whole process heat integration. However, due to the technical barriers, it is always a challenge to design the heat integration system while optimizing the process parameters by mechanistic models. In response to this issue, this study presented a novel surrogate model-based framework that allows for the seamless integration of process optimization and heat exchanger network (HEN) design. The EO production process is modeled and simulated to provide the essential data for surrogate model training. Considering the inherent complexity of the process and the challenges associated with model training, the whole production process is decomposed into parts and the output parameters relevant to heat integration are included within the surrogate models training by Artificial Neural Network. Building upon these preliminary steps, a flexible optimization framework built upon the Genetic Algorithm, integrating the developed process surrogate model and any HEN synthesis model, is constructed to achieve synchronous optimization. The results show that the obtained process saves 22.93 % utility cost and finally leads to a 2.60 % increase in total profit than the alternative designed by the conventional stepwise method, showing the priority of the proposed method.

Integrated CO2 capture and conversion into methanol units: Assessing techno-economic and environmental aspects compared to CO2 into SNG alternative

Using carbon dioxide (CO2) as a raw-material to produce value-added chemicals has a strategic role to play in the decarbonization of energy resources and the transition to a climate-neutral economy. E-methanol, Synthetic Natural Gas (SNG) and e-kerosene are one of the most promising pathways to convert CO2. In this context, the aim of this work is to propose an optimized and integrated CO2 to methanol process and then to compare it to the CO2 to SNG process from economic and environmental points of views. An optimized reactor configuration in the CO2 to methanol conversion unit has been successfully implemented in Aspen Plus® and leads to a thermal energy self-sufficiency of this unit. A heat integration with an advanced capture unit has been performed where 5 % of the heat requirement could be provided from the conversion unit while 95 % come from external steam source. Techno-economic assessment of the optimized process showed that methanol is more profitable when it is used as a raw material to synthetize other chemicals. As an energy carrier, SNG is more interesting. Compared to the reference scenario, a net CO2 emission reduction of 70 % in the CO2 to SNG route and of 60 % in the CO2 to methanol route were obtained. Concerning the fossil depletion impact, in both cases, a reduction of more than 60 % was noticed (ca. 75 % in CO2 to SNG route and 61 % in CO2 to methanol case).

Heat pipe solar collectors: A Review

Abstract In today’s world, the consumption of energy is quickly growing, and the exhaustion of non-renewable energy sources poses a significant risk to the entire human race. The importance of renewable energy sources emerged as a result of this, and solar energy is currently considered to be among the most promising and significant sources of clean and renewable energy. There has been a significant amount of work done in the field of solar radiation harvesting in order to make the most of it. This was accomplished by substituting the standard solar collectors, which are lacking in certain elements of performance and have a lower efficiency, with a modified solar collector that is superior to the normal collectors. Among the many modifications that can be made to the solar collector, the heat pipe is particularly significant. This review will present a variety of studies on the modification of heat pipe solar collectors (HPSCs) construction and integration within the systems, as well as an analysis of the performance enhancements that were made to it. Additionally, we provide a wide range of applications that make use of solar collectors that are shaped like heat pipes. In conclusion, we offered some suggestions for potential developments in the field of heat pipe solar collectors with regard to future trends.

Optimization of Energy Consumption in Formaldehyde Production Process Using Reboiled Absorption Process

Formaldehyde is a crucial chemical building block in various industries, and its production often involves energy-intensive processes. This study focuses on optimizing energy consumption in formaldehyde production, explicitly employing the reboiled absorption process with a production capacity of 27,000 tons per year. The objective of this article is to develop a more energy-efficient process of formaldehyde synthesis by addition or refrigerant cycle stream to preserve the energy, reducing energy consumption and improving the sustainability of the process. The reboiled absorption process involves the absorption of formaldehyde gas into a liquid absorbent, followed by reboiling to release the absorbed formaldehyde. A comprehensive analysis of the entire production system compares unmodified and modified process simulations, heat integration, and energy analysis. Beside the energy consumption of the process, the number of stages within the absorption process contributes to the product mass flow rate of the overall process by increasing the surface area which mass transfer can occur. However, adding too many stages to the process may negatively impact the energy efficiency of the process. Therefore, optimizing energy consumption and absorption processes in formaldehyde production is essential to improve the sustainability of the process and increase the overall profitability of the production process. The results show that the proposed method dramatically improves the sustainability of CH2O synthesis by reducing overall energy consumption and emissions by 93.978%, reducing energy consumption from 153,735,360.4 kJ/h to 9,256,646.618 kJ/h. Copyright © 2024 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Efficient simultaneous optimization approach for the synthesis of large-scale heat-integrated water networks

This study develops a generalized superstructure and a compact mixed-integer nonlinear programming (MINLP) model for achieving efficient energy and water utilization in designing integrated process water systems with large sizes. Utilizing non-isothermal mixing reduces the need for many heat exchangers for indirect heat recovery. Hence, an exchanger-centric modeling strategy for heat integration is embraced over a hot–cold streams matching-based approach. A novel two-step approach is proposed to address the nonconvex and nonlinear challenges and ensure the efficiency of getting high-quality solutions. Initially, a targeting model incorporating linear heat integration is adopted to reduce the superstructure and partially initialize the design model. Subsequently, in the synthesizing stage, a two-level global search procedure is devised, integrating adaptive exchanger adjustment with multi-start local optimization. The robustness and efficiency of the proposed approach are confirmed through the resolution of four large-scale problems within one hour, yielding improved results compared to the best-known existing solutions.

Modeling of a heat-integrated biomass downdraft gasifier: Influence of feed moisture and air flow

A model for a heat-integrated biomass downdraft gasifier is developed and used to study the influence of changes in biomass moisture content and gasifier air flow. This one-dimensional steady-state model accounts for pyrolysis, combustion and gasification reaction kinetics as well as transport phenomena occurring within the gasifier and heat integration system. The gasifier is divided into four zones for solving the ordinary differential equations (ODEs), because each zone has different geometry for the reactor or heating system. The material and energy balance ODEs are solved as a boundary value problem (BVP), ensuring that conditions for the producer gas at the bottom of the reactor match the conditions of the countercurrent annulus gas, which is used for heating. The model also accounts for the preheating of the biomass using exhaust gas from an associated engine used to generate electricity from the producer gas. The model predicts the process gas temperature, flow rate and composition and was validated using two experimental runs with different control inputs. The model predictions show good agreement with the data. Simulations with the highest feed moisture result in lower reactor temperatures and simulations with the highest air flow result in the highest reactor temperatures.

Multi-criteria study and optimization of an innovative combined scheme utilizing compressed air energy storage for a modified solid oxide fuel cell-driven gas turbine power plant fueled by biomass feedstock

This paper explores the potential of a combined solid oxide fuel cell and gas turbine technology for medium- to large-scale power generation, emphasizing its applicability and sustainability, particularly with biomass feedstock. An innovative heat integration process is developed for a modified solid oxide fuel cell and gas turbine power plant, incorporating a steam power cycle, compressed air energy storage, a Kalina cycle, and a domestic hot water production subsystem. The system utilizes biomass through a downdraft gasifier, enabling a comprehensive evaluation of thermodynamic, economic, and environmental performance during both charging and discharging phases. A detailed parametric sensitivity analysis is performed to investigate two operational modes. Subsequently, five multi-objective optimization scenarios are formulated and optimized using the cuckoo search algorithm and two decision-making approaches. The results indicate that the optimization scenario focusing on exergetic round-trip efficiency and the unit cost of products during the discharging phase achieves superior thermodynamic and environmental performance. Specifically, the system exhibits energetic and exergetic round-trip efficiencies of 59.20 % and 51.06 %, respectively, with a levelized total emission of 0.64 kg/MWh. Furthermore, when considering the objectives of exergetic round-trip efficiency and net present value, the optimal economic performance is achieved with a payback period of 1.54 years and a net present value of $7.44 million.

Blockchain-based concept for total site heat integration: A pinch-based smart contract energy management in industrial symbiosis

Industrial symbiosis has gained prominence in pursuing sustainable industrial practices, aiming to optimise resource utilisation and reduce environmental impacts. A critical aspect of this endeavour is the efficient management of energy resources within an industrial ecosystem. This paper presents a novel approach to enhance Total Site Heat Integration (TSHI) implementations by employing Blockchain as a facilitator for decentralised energy management. TSHI is an efficient and widely applied method for industrial symbiosis concerning energy flows, which employs the steam mains in site utility systems as the platform for exchanging heat between industrial processes at various temperature levels. It is shown that the synergy of Pinch Analysis and Smart Contract technologies is capable of facilitating energy integration of processes belonging to independent market actors, compared with the currently dominant integration inside a single company. The proposed framework leverages Blockchain as a distributed ledger to enable secure, transparent, and automated energy management across multiple industrial entities in an industrial symbiotic network. The integration of Pinch Analysis principles ensures that the Heat Integration process is optimised to improve the overall energy efficiency. Smart contracts enable automatic negotiation and execution of energy transactions based on predefined rules, minimising the time lag for concluding deals on energy resource exchange and conservation. This paper examines several scenarios to illustrate the implementation of the proposed Blockchain-based TSHI concept within an industrial symbiosis network. It is demonstrated that up to 16 % cost savings are possible by simply enabling transparency via Blockchain. The results could drive innovative development to revolutionise decentralised energy management in a complex industrial ecosystem, especially by synchronising energy exchanges in time.

Multiscale Equation-Oriented Optimization Decreases the Carbon Intensity of Shale Gas to Liquid Fuel Processes.

Shale gas is revolutionizing the U.S. energy and chemical commodity landscape and can ease the transition to a sustainable decarbonized economy. This work develops an equation-oriented (EO) multiscale modeling framework using the open-source IDAES-PSE platform that tractably incorporates microkinetic detail in process design via reduced-order kinetic (ROK) models. Using multiobjective optimization with embedded heat integration and life-cycle analysis, we simultaneously minimize the minimum selling price of liquid hydrocarbons (e.g., liquid fuels/additives from shale gas) and process emissions (via a CO2 tax). Optimization reduces greenhouse gas emissions per MJ of fuel produced by over 35% compared to the literature and achieves a carbon efficiency of 87%. The optimizer changes the recycling rate, temperatures, and pressures to mitigate the effect of ROK model-form uncertainty on product portfolio predictions. Moreover, we show that the optimal process design is insensitive to changing CO2 tax rates. Finally, the EO framework enables a fast sensitivity analysis of shale gas composition variability across 12 regions of the Eagle Ford basin. These results highlight the benefits of the open-source EO framework: fast, scalable, customized, and reproducible system analysis and optimization for sustainable energy technologies beyond shale utilization.

Synthesis of heat-integrated water networks: Integration of heat pumps

A typical heat-integrated water network (HIWN) synthesis problem aims to minimise freshwater and utility consumption while establishing trade-offs between operating and investment costs by exploring different water and heat integration opportunities. Heat integration between hot and cold water streams is performed to save external heating and cooling utilities required to achieve the target temperatures of these streams. This paper proposes a mathematical programming approach to integrate water-to-water heat pumps into the HIWNs. A simple cascade heat pump system with isobutane as a natural working fluid enables a larger temperature lift between the heat pump source and the sink. The objective function of the proposed mixed-integer nonlinear programming (MINLP) model is to minimise the total annualised cost (TAC). The TAC includes operating costs for freshwater, heating/cooling utilities, electricity, and investment in heat exchangers and heat pumps. A sensitivity analysis is performed to evaluate the economic feasibility of the system by varying the heating/electricity cost ratio and depreciation period for the capital investment. The results show that additional utility savings can be obtained by integrating heat pumps into the HIWNs. For threshold problems, a heat pump is feasible for heating/electricity price ratios from 1.175, and heating utility is replaced by electricity for a 1:1 ratio. However, for pinched problems, the feasibility of the heat pump is shifted to lower heating/electricity price ratios, from 0.3 to 0.5, depending on the annualisation factor for the investment.

Potential of treated wastewater as an energy source for district heating: Incorporating social elements into a multi-factorial comparative assessment for cities

Recovering waste heat from urban infrastructures is gaining greater importance in the context of decarbonisation. However, evaluating the feasibility of waste heat recovery projects requires a holistic analysis of potential impacts, which includes social elements that are often overlooked. This paper introduces a novel methodology for assessing the competitiveness of waste heat integration into district heating, based on a multi-factorial decision support tool that incorporates energy poverty as a key performance indicator, in addition to energy, environmental and economic factors. The comparative assessment is based on the implementation of large-scale heat pumps recovering wastewater heat, a resource of great potential that is still underutilised in Europe. The methodology is tested in the cities of London and Riga, which are in countries with significantly different stages of DH development. In London, an emerging market with high growth potential, and in Riga, where there is a well-established DH system. The study has shown that waste heat can significantly reduce consumers' bills for heating, which was observed in all analysed scenarios. The social benefit decreases when the replaced technology involves biomass heat-only boilers or combined heat and power. The methodology presented is generic and can be applied to other locations and heat sources.